I've been spending many hours with
Pinball Arcade... it's an emulator that lets you play the best real world pinball tables (Bally, Williams, Stern and Gottlieb.)
You buy packs of tables (each with the complete soundtrack and ROM) as an in-app purchase so if you try to Pokémon them, it's going to be expensive. However, just a single table should last you for a very long time - these classic tables have more 'content' than many software-only designs... I feel it's worth the price.
The controls aren't optimal for phones (and you can get some performance issues) but it works perfectly on tablets.
I'm currently playing: